Means for checking superposed impressions on a moving web



Allg- 1954 J. BOGERT 2,686,453

J. MEANS FOR CHECKING SUPERPOSEID IMPRESSIONS ON A MOVING WEB Filed Aug. 1, 1950 6 Sheets-Sheet l INVENTOR John, Jfiqgefii' BY flaw ATTORKI EYS Aug. 17, 1954 J. J. BOGERT MEANS FOR CHECKING SUPERPOSED 2,686,453 IMPRESSIONS ON A MOVING WEB 6 Sheets-Sheet 2 Filed Aug. 1, 1950 mm mm mm mm 1954 J. J. BOGERT 2,686,453

MEANS FOR CHECKING SUPERPOSED IMPRESSIONS ON A MOVING WEB Filed Aug. 1, 1950 6 Sheets-Sheet 3 |Fl H INVENTOR ATTORN Aug. 17, 1954 J. J. BOGERT MEANS FOR CHECKING SUPERPOSED IMPRESSIONS ON A MOVING WEB 6 Sheets-Sheet 4 Filed Aug. 1, 1950 ATTORNEYS R m N Mm -M 0 J Aug. 17, 1954 J. J. BOGERT MEANS FOR CHECKING SUPERPOSED IMPRESSIONS ON A MOVING WEB 6 Sheets-Sheet 5 Filed Aug. 1, 1950 INVENTOR Johndfloyefii ATTORNEYS Aug. 17, 1954' J. J. BOGERT 2,686,453

MEANS FOR-CHECKING SUPERPOSED IMPRESSIONS ON A movms was 6 Sheets-Sheet 6 Filed Aug. 1, 1950 INVENTOR Jblirz Jfiqgerb Patented Aug. 17, 1954 MEANS FOR CHE CKING SUPERPGSED IMPRESSIONS ON A MOVING WEB John J. Bogart, Fairlawn,

N. J., assigncr to National Laboratories Manufacturing Corp., a

corporation of New J erse Application August 1, 1950, Serial No. 177,003

Claims. 1

This invention relates to an apparatus for observing repeated patterns or designs on a moving web and more particularly for inspecting the registration, quality and .color of a plurality of superposed printed impressions which form the design.

As conducive to an understanding of the invention, it is noted that in the printing of repeated multi-colored designs on a continuous web, the diiierent color impressions which form the final design are printed successively in superposed relation from a nunber of printing rollers.

In order to provide high grade printing it is necessary that the various impressions forming each design be in registry and properly aligned. It is therefore desirable that an inspection be made of the alignment and registration of the printed impressions in order that defective desi ns will not be produced. As the web is movat a relatively high speed, such inspection direct observation of the printed web is impossible mechanism is provided, which may be of the type shown in the patents to l-iorton Nos. 2,14'Ld92 2,155,613, whereby successive identical areas on the printed, moving web are reflected for a period of time by a suitable refleeting m mber which is moved in synchronization with th running web so that the printed impressions on such areas will appear stationary and thereby permit close inspection thereof.

he e the design to be inspected is relatively arg the area viewed at any one time may only a portion oi the entire design and it is desirable thatmeans be provided to permit any portion of the design to be inspected.

Where a mirror is rotated in synchronization with the movement of the web, such as by of a worm and worm gear drive and the relative position or" the worm with respect to the Worm gear changed to advance or retard the mirror slightly with respect to the synchronous speed of the web and the mirror, although inspection of the entire design is aiforded, it has been found that the errors in lead inherent in the gears cause objectionable error in tracking that result in an apparent jiggling of the reflected area.

As the superposed impressions in such reflected may be small size, the jiggl r may make impossible to determine if such presus a e in re istry and hence no accurate inction can be in de without stopping the movement of the web which would cause an objectionable slowing of the output or" the printin machine.

It is accordingly among the objects of the invention to provide a viewing apparatus which is simple to operate and install and has but relatively few parts, none of which is likely to become out of order, and with which device an observer may view the reflected image of any selected portion of a design formed by means or" a plurality of superposed printed impressions on a web or scan the entire design at any selected rate of speed with substantially no jiggling in the reflected image of such design, regardless of the area being viewed, so that even the smallest impression may be minutely checked, and which device when once adjusted for maximum accuracy does not become out of adjustment.

Where the mirror used the scanning apparatus is rotated by means of a Selsyn motor coupled in conventional manner to a second Ezelsyn motor driven in synchronization with the printing rollers, an element of oscillation or hunting is inherent in the operation of the first mentioned Selsyn motor with the result that the reflected image swings back and forth over a given point rendering it difficult to inspect.

It is accordingly another object to provide a selsyn motor drive in a viewing apparatus of the above type in which there is a minimum of hunting in the driven Selsyn motor with resultant steadiness of the image.

As it is essential with Selsyn motors that they maintain synchronization even during acceleration, the use of a relatively heavy flywheel is desirable, but the inertia of such flywheel on the driven Selsyn motor may result in stalling before it can accelerate to full speed unless Selsyn motors so large are used as excessively to increase the cost and hull: of the apparatus.

It is accordingly still another object to provide an apparatus of the above type in which the hywheel mass is applied to the shaft of the driven Selsyn motor in such manner as not to overload the latter.

According to the invention, a substantially cylindrical drum is provided having a plurality of identical longitudinally extending mirrors on the periphery thereof the lengths of which extend across the web and desirably form a regular polygon in transverse cross section. The drum is desirably rotated by a gear transmission, preferaby one of the worm gear type driven by a Selsyn motor which in turn is preferably driven by a driving Selsyn motor that is coupled to the printing rollers, so that the two Selsyn motors may be driven in synchronization with the printed web, a differential Selsyn motor being interposed between said two Selsyn motors to change the movement of the driven Selsyn motor in a predetermined manner relative to that of the driving Selsyn motor so that any selected area of the design on the web may be viewed or, if desired, the entire design may be scanned.

Desirably the driven Selsyn motor has a fly-- wheel thereon to reduce the hunting inherent in Selsyn motor systems and such flywheel is desirably coupled to the Selsyn motor shaft in such manner as to preclude excessive load and possible stalling in the course of bringing such driven Selsyn motor up to speed.

In the accompanying drawings in which are shown one or more of various possible embodiments of the several features of the invention,

Fig. 1 is a diagrammatic side elevational View of the apparatus,

Fig. 2 is a fragmentary side elevational view similar to Fig. l on a larger scale partly in cross section and with parts broken away,

Fig. 3 is a fragmentary side elevational view of the opposite side of the apparatus to that shown in Fig. 2,

Fig. 4 is a fragmentary front elevational view of the apparatus with parts broken away,

Fig. 5 is a fragmentary transverse sectional view of the apparatus with parts broken away taken along line 5-5 of Fig. 2,

Fig. 6 is a fragmentary longitudinal sectional view of the apparatus taken along line 6-5 of Fig. 5,

Fig. '7 is a detail sectional view on a larger scale taken along line ll of Fig. 4,

Fig. 8 is a sectional View on a larger scale taken along line 8-8 of Fig. 3, r

Fig. 9 is a diagrammatic view illustrating the operation of the apparatus, and

Fig. '10 is a diagrammatic circuit diagram of the Selsyn motors.

Referring now to the drawings, in Fig. 1 is shown a diagrammatic side elevational view of the apparatus which desirably comprises a supporting frame which may include a pair of spaced parallel uprights or beams l2 mounting transversely aligned pairs of laterally extending brackets l3 and M.

Rotatably mounted on each pair of brackets 53 and 14 are transverse guide rollers l5 and it around which the printed web I'l passes. As shown in Fig. 1, one end of the web is wound around a roll it! to be collected thereon and, the other end of the web I? is fed from a supply roll 19 and passes between a plurality of pairs of printing rollers 2i and 22, only one of which is shown, the pairs of rollers successively printing the impressions which form the completed design. Desirably each of the pairs of brackets is and M carries a lamp 2% thereon to illuminate the vertical portion 24 of such web which is stretched between rollers !5.

Also mounted on the beams l2 between brackets l3 and I l are a pair of spaced parallel, horizontal tracks 25 and 26 supported adjacent their ends by braces 21, and which serve as the mount for a housing 3i containing the scanning mechanism for viewing the web ll.

Although the scanning mechanism may be of any suitable type, it desirably comprises a drum 32 extending transversely of the housing 35 and rotatably mounted therein between the spaced upright side plates 33 and 33.

As shown in Fig. 5, the drum may comprise a pair of hubs 35 and 36 retained in spaced parallel relation by separator bars Bl held'against the hubs by screws it. The drum 32 desirably carrice a plurality of light reflecting surfaces or mirrors 38 which are desirably elongated flat strips of uniform length and width afliXed at their ends by brackets 39 to the periphery of hubs 35 and 36.

As shown in Fig. 6, the adjacent longitudinal edges ll of the mirrors 38 are desirably beveled and are retained in edge to edge abutment preferably of their thickness. The peripheries of hubs 35 and 3t desirably have a plurality of flats 42 thereon against which the associated ends of the mirrors may rest, the mirrors 38 thereby forming a regular polygon in cross section.

Although the mirrors 38 could be of any suitable type, it is preferred to have them coated on the front surface thereof. Such mirrors are advantageous in that they eliminate the double reflection inherent in conventional rear surface mirrors which prevents clear definition of the impressions to be viewed and in addition as the physical mounting of the flat mirror strips upon a drum necessitates a joint at the adjacent mirrors, the visual effect of these joints is minimized, for if back surface mirrors should be employed, the rays of light would have to pass through the glass and return, with resultant loss of definition at each joint due to parasitic reflections.

Means are desirably provided to rotate the drum 32 in synchronization with the rotation of the printing rollers 2i and 22 and the movement of the web ll. To this end, each of the hubs 35 and as desirably has an axial hub bearing 4 affixed as by set screws (not shown) to a transverse shaft lb which extends therethrough. The shaft 55 is desirably journalled at one end in a bearing block 46 affixed to the inner surface of plate 33 and near its other end in a bearing block ll affixed to the outer surface of plate 3 The end 43 of shaft 45 which extends through bearing block ll desirably has a worm gear 49 aflixed thereon which meshes with the worm 5i aflixed on the drive shaft 52 of a Selsyn motor 53 mounted on the outer surface of plate Ed, said shaft 52 being journalled in a laterally extending bearing block 5d affixed on plate 34.

The Selsyn motor 53 is electrically connected in conventional manner to a driving Selsyn motor 55 to be driven thereby, said Selsyn motor 56 being driven through gearing 5'! (Fig. 1) from the printing roller 22, the Selsyn motors functioning in the mamier well known in the art, so that upon rotation of the rotor of the driving Selsyn motor the rotor of the driven Selsyn motor will be rotated a corresponding amount.

In order to view the impressions reflected from the vertical portion 24 of web ll to the mirrors 3% in th manner hereinafter to be described, a mirror 59 is desirably provided which, as shown in Figs. 5 and 6, is desirably an elongated strip extending parallel to drum 32 and mounted between plates .53 and 34 so a to oscillate or rock back and forth to maintain unaltered the optical relationship between the moving web area being viewed and the reflected image projected to the observer.

As shown in Fig. 6, the mirror 5c is clamped to a rigid strip preferably of metal, having a longitudinal reinforcing rib 52 on the undersurface thereof. The clamping is desirably effected by means of clamp bars 53 and as extending transversely across the mirror 5?; at it ends, said clamp bars being retained together by screws 55. Each of the clamp bars 33 desirably has a hub 66 aflixed thereto on the outer surface thereof so that the axis of each of the hubs is aligned with the top surface of the mirror 59 midway between its side edges. The mirror 59 is mounted between the side plate 33 and 34 by means of bearing pins 6'! rigidly alfixed to sa d plates and extending laterally inward therefrom through the hubs B6 of the clamp bars 63 and is desirably rocked by a lever 59 (Fig. 6) one end of which is afrixed to hub it while the other end carries a cam roller ll resiliently retained as by a coil spring '52 in engagement with the periphery of a cam 73 affixed by screws it to hub 36.

As both the mirrors 38 on the drum 32 and the oscillating mirror 59 etxend the entire width of the web ll, it is apparent that a design that extends over such entire width will be reflected so that it may be seen by an observer viewing mirror 59.

In order to permit minute inspection of such design, magnifying means may desirably be pro vidcd which may comprise a pair or binoculars ll mounted on a carrier 1'8 movable transversely between side plates 33 and 34 on a transverse guide rail l5. When any portion or the web is to be observed, the carrier 8 is moved to the selected position on guide rail 15 and fixed in place by set screw 16 and the binoculars Tl may be fcused as desired.

With the construction thus described, it is apparent that the drum 32 at a predetermined distance from the vertical portion 24 of the moving web ll, as shown in Fig. 9, one of the mirrors, e. mirror 38, will reflect the area on the web portion 2 indicated by the point id. The image from point it will be reflected from mirror 38 to mirror so that it can be seen by the observer through binoculars Ti.

As the drum 32 rotates in a clockwise direction and the web 11 moves in the direction of the arrow, the mirror 38' will follow point 18 until such mirror moves past the line of sight 79 of the binoculars "ii at which time the beginning or the next mirror 38" comes into the line of sight 19 of the binoculars ll.

As successive identical patterns on the web are equi-distantly spaced thereon by an amount which will will bring one pattern into sight immediately after the preceding observed pattern passes out of sight, the observer will see what is apparently a stationary object.

Inasmuch as an element of hunting or oscillation is inevitable in Selsyn motor connected as above described, such hunting of the Selsyn motor 53 would cause the image seen to swing back and forth about a fixed point thereby rendering minute inspection thereof diilicult.

It is therefore desirable to mass to the shaft 52 of the driven Selsyn motor 53 to act as a flywheel for substantially constant speed rotation without hunting. Because of space limitation, a single flywheel of large size has been found to be impractical and it has been found desirable, in order to achieve the desired mass with a minimum of size, to provide a pair of relatively small flywheels Bi and 82. As shown in Fig. 2 flywheel 8! is mounted on shaft 52 desirably has encompassing pulley belt 83 which drives a pulley 3 aflixed on countershaft 85 join-nailed in laterally extending brackets 88 and El ailixed to plate as, the end 38 of shaft 55 having said flywheel 82 aiiixed thereon. Preferably the pulley 8 has a much smaller diameter than flywheel 8! so that flywheel 82 will rotate at a greater speed than flywheel 3 l As the inertia of flywheels 8| and 82 is relaill tively high, it would require the application of considerable torque in order that the Selsyn motor 53 may accelerate to the speed of the driving Selsyn motor 56, and consequently the Selsyn motor 53 would have to be of relatively large size, which in addition to being very expensive would occupy considerable space.

In order to use a moderately sized Selsyn motor, yet with the required flywheel mass to prevent hunting, means are desirably provided to permit the Selsyn motor 53 to attain substantially its running speed before the full mass of the flywheels 8i and 82 is applied thereto. To this end as shown in Fig. 2, a friction clutch 9! is desirably interposed between shaft 52 and flywheel 82. The clutch may comprise an inner bearing race 92 affixed on the end of shaft 52 and coasting with an outer race 93 ailixed to the wall of an axial bore iii in the flywheel 8|. The end face 95 of the flywheel 3! desirably has a friction ring urged thereagainst by a resilient plate at amxed at its axis as by screws 538 threaded into the end of shaft 52.

Thus, upon initial rotation of shaft 52, due to the inertia of flywheels 8! and 82, plate 9] will slide on ring 58 applying but little driving torque thereto, and hence flywheels 8| and 82 will initially rotate very slowly with but little load being applied to shaft 52. As shaft 52 and flywheels 3i and 82 continue rotating, the flywheels will gradually build up to their normal running speed with their load being gradually applied to shaft 52 so that Selsyn motor 53 may come up to the speed of the driving Selsyn motor 56 Without stalling, which might occur if the load of the flywheels was suddenly applied. Thus, the two Selsyn motors 53 and 56 will remain in synchronization.

It is to be noted that the vertical range of coverage of the web by the reflecting mirrors 38 on drum 32, depends upon the distance of said o e from the web, for the angle embraced esp the upper and lower dot and dash lines iiil in Fig. 9 is determined by the number of mirror faces on drum 32 and does not change. Consequently the mirrors 38 must be spaced a predetermined distance from the web in order that identical areas on the successive identical printed designs on the web may be viewed.

Where the printing cylinder '22 carries one design about its periphery, the mirrors 38 and the web must be spaced by a certain amount. Where cylinder 22 has two identical designs in sequence about its periphery each extending half way around, the impressions will occur on the web twice the frequency they would occur if but one resign extended around the cylinder. In such latter case it is desirable to reduce the distance between the mirrors 38 and the web IT so that but a single design will be reflected to the mirrors 38 and as the web I? will be closer to the observer the design may be more closely inspected. To afford such movement, the housing 3! desirably has one pair of transversely aligned rollers liii rotatably mounted near the rear edge of each of the upright plates 33 and 36 riding on tracks 25 and 25 respectively, and a second pair of transversely aligned. rollers I02 rotatably mount d on the protruding ends of a transverse shaft I63 extending through the plates and 3 3 front lower edge thereof, said rollers Elli. also riding on rails 25 and 25 respectively.

Each of the tracks has a rack H14, affixed on its outer surface and extending longitudinally thereof, which racks are engaged by pinions I06, I01 respectively aifixed to the ends of shaft I03 and riding on said racks.

In order to rotate said shaft I93 to effect movement of the housing SI, a worm I68 is desirably provided which meshes with a worm gear III affixed on the end of the shaft m3 adjacent pinion IIl'I. Worm I03 is preferably affixed on a shaft II2 journalled in brackets as and 81 and having a handwheel H affixed on the forward end thereof extending through the front wall H3 of protective housing II l. Thus, upon rotation of the handwheel H5 in either a clockwise or counterclockwise direction, the housing 3! may be moved back or forth as desired.

Since as previously pointed out and as diagrammatically shown in Fig. 9, only a relatively small area lengthwise of the web can be viewed by the observer, it is desirable to permit inspection of any portion 'of the design especially where the design covers a considerable portion of the length of the web. To this end means are provided to change the phase of the driven Selsyn motor 53 with respect to the driving Selsyn motor 56 either momentarily or continuously so that the position of the mirror 38 on drum 3'2 rotated by Selsyn motor 53 with respect to the moving web may be changed, thereby to bring another area of successive designs on the moving web into view or to continuously scan the designs.

To accomplish such result, in the embodiment herein shown, a differential Selsyn motor IZI, electrically connected in conventional manner as diagrammatically shown in Fig. 10, is interposed between the driven Selsyn motor 53 and the driving Selsyn motor 56. The differential Selsyn motor shaft I23 desirably has a worm gear I24 thereon which meshes with a worm I 25 afiixed on a shaft I25 extending parallel to side plate 33. Shaft I25 which extends through front wall I21 of a protective housing I28 is manually rotated by a handwheel I29 and desirably is journalled in a bearing block I3I on wall I2? and in a bearing block I32 extending laterally outward from plate 33.

With the above construction, a viewer by merely rotating the handwheel I29 will turn the rotor of the differential Selsyn motor I2l, which functions in conventional manner, to cause the rotor of the driven .Selsyn motor 53 to be advanced or retarded with respect to the rotor of the driving Selsyn motor 56 depending upon the direction of rotation of the hand wheel I29. As a result, the angle of the mirrors 38 on the rotating drum with respect to the web will be changed to permit any area of the design to be inspected.

Means are also desirably provided automatically to rotate shaft IZE to provide for continuous scanning of the entire design.

For this purpose a motor I35 is desirably provided as shown in Fig. 3, afiixed to plate 33 and which, through a reduction gear drive I36 rotates a pulley iSI. By means of a pulley belt I38 the pulley rotates a clutch ring I39 shown in Fig. 8, rotatably mounted on the reduced end MI of a complementing clutch member I42 which is rigidly aifixed to the end of shaft I26. The shoulder I53 formed by the reduced and of clutch member I42 is desirably beveled as at Md and a resilient friction ring I45 encompasses said clutch member being seated on said beveled portion Md and resting against the adjacent face I46 of ring I39.

Thus, upon rotation of shaft I26 by handwheel I29, the gear transmission I36 will provide sufficient load on clutch ring I39 so that by reason of the slipping friction ring I45, shaft I25 may turn freely. However, upon rotation of the clutch ring I39 by motor I35, the ring I45 will provide sufficient frictional engagement to drive clutch member I 32 thereby to rotate shaft I26 and through the gear transmission previously described to rotate the differential Selsyn motor IZI.

With the apparatus thus described, an optically stationary image of the moving web is attained, which may readily be inspected. It is apparent that if a stationary image of a sample of material is brought visually adjacent the web, a means of comparison is achieved.

To this end a color comparator is provided comprising an arm I5I which extends longitudinally between side plate 33 and 3E. The front end of the arm ISI is affixed as at I52 in Fig. 4 to a carrier I53 slidably mounted on transverse guide rail 75, said carrier being retained in any position of adjustment by a set screw I55. The arm i5 I, as shown in Fig. 6, desirably has reflecting mirrors I5? mounted thereon adjacent the oscillatory reflecting mirror 59, said mirrors I51 being positioned so as to reflect rays of light, desirably to the binoculars ii, from a sample of material which may be positioned adjacent the moving web in any suitable manner.

As the two reflecting surfaces of the drum and the oscillatory mirror tend to discriminate slightly between light rays of different wave length, thereby creating a slight color change, in order to compensate for this color change so that an accurate comparison may be made of the sample of material and the impression on the web, two reflecting mirrors I5? are utilized, desirably of the same type as the reflecting surfaces or the drum and the oscillating mirror. Thus if the printed impression and the sample are identical they will so appear when viewed through the mirrors of the comparator, whereas if no reflecting mirrors IE'I were used, even though the sample of material and the printed design should be identical in color, the color change caused by the mirrors 3% and 59 would prevent accurate comparison.

Thus, it is a relatively simple matter for the observer, when he desires to compare the sample of material with the printed impression, to move the carrier I53 along transverse guide rail I5 to any desired position so that the sample will be positioned adjacent the portion of the impression to be compared. By then looking through the binoculars 5?, the apparently stationary impression on the web may be readily compared with the stationary sample.

With the construction thus described, a highly efiicient viewing apparatus is provided whereby any portion of a repeated design on a moving web may be maintained in apparently stationary position with substantially no jiggling or other movement, thereby facilitating minute inspection thereof.

As many changes could be made in the above construction, and many apparently widely differentembodiments of this invention could be made without departing from the scope ,of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

- 1. An apparatus for observing successive printed designs equi-distantly spaced on a moving web, comprising a rotary reflecting member having a plurality of light reflecting surfaces extending across such web, observing means positioned to view said reflecting member, a first Selsyn motor to drive said rotary member successively to present said light reflecting surfaces by its rotary movement to receive and reflect successive light rays from the moving designs, a second Selsyn motor electrically connected to said first Selsyn motor, means to rotate said second Selsyn motor in synchronization with the movement of said web thereby to rotate said first Selsyn motor in synchronization with the movement of said Web, a differential Selsyn motor electrically connected between said first and second Selsyn motors, means to rotate the rotor of said differential Selsyn motor to change the phase of said first Selsyn motor in predetermined manner with respect to the phase of said second Selsyn motor thereby to adjust the relative position of said light reflecting surfaces with respect to said web, means to move a portion of such printed web in a straight observable path and means to observe an area adjacent the portion of such web moving in a straight observable path, said means comprising an arm, a pair of inclined reflecting mirrors on said arm, one of said mirrors having its reflecting surface directed towards such area adjacent the web to reflect rays of lights therefrom onto said second mirror, and said second mirror having its reflecting surface directed toward said observing means to reflect the rays of light thereto.

2. An apparatus for observing successive printed designs equi-distantly spaced on a moving web, comprising a rotary reflecting member having a plurality of light reflecting surfaces extending across such web, a first Selsyn motor to drive said rotary member successively to present said light reflecting surfaces by its rotary movement to receive and reflect successive light rays from the moving designs, a second Selsyn motor electrically connected to said first Selsyn motor, means to rotate said second Selsyn motor in synchronization with the movement of said web thereby to rotate said first Selsyn motor in synchronization with the movement of said web, a differential Selsyn motor electrically connected between said first and second Selsyn motors and means to rotate the rotor of said differential Selsyn motor to change the phase of said first Selsyn motor in predetermined manner with respect to the phase of said second Selsyn motor thereby to adjust the relative position of said light reflecting surfaces with respect to said web, said means comprising a control shaft, means operatively connecting said control shaft to the rotor shaft of said differential Selsyn motor, a hand wheel at one end of said control shaft to rotate the latter, a clutch at the other end of said control shaft and a drive motor operatively connected to said clutch to rotate said control ;and when said drive motor is energized said con- ,trol shaft will be rotated.

3. The combination set forth in claim 2 in -,which said clutch is of the friction type comprising a member aflixed to said drive shaft and having a reduced nose portion forming a beveled shoulder, a friction ring encompassing said reduced nose, and a complementary clutch ring rotatably mounted on said reduced nose portion, said friction ring engaging said beveled shoulder and the opposed face of said clutch ring, the latter being rotatable by said drive motor.

4. An apparatus for observing printed impressions on a moving web, comprising a rotary refleeting member, a worm wheel operably connected to said member, a first Selsyn motor having a drive shaft, a worm affixed on said shaft in mesh with said worm wheel, a second Selsyn motor electrically connected to said first Selsyn motor, means to rotate said second Selsyn motor in synchronization with the movement of such web thereby to rotate said first Selsyn motor in synchronization with the movement of such web, a flywheel associated with the drive shaft of said first Selsyn motor to prevent hunting thereof with respect to said second Selsyn motor, a friction clutch interposed between said drive shaft and said flywheel, a second flywheel associated with said first flywheel and driven thereby, and means interposed between said flywheels to drive said second flywheel at a greater speed than said first flywheel.

5. The combination set forth in claim 4 in which said rotary reflecting member comprises an elongated drum extending across the moving web, and said light reflecting surfaces comprise a plurality of reflecting strips affixed on said drum and forming a regular polygon thereon, said strips being successively presented by the rotary movement of the drum to receive and reflect in succession light rays from the impressions on the moving web, each of said reflecting strips comprising a mirror having a reflecting coating on the front surface thereof.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,140,402 Horton Dec. 13, 1938 2,155,013 Horton Apr. 18, 1939 2,184,750 Meinhardt et a1 Dec. 26, 1939 2,214,500 Fischer Sept. 10, 1940 2,344,296 Frink Mar. 14, 1944 2,454,959 Barnes Nov. 30, 1948 OTHER REFERENCES Lauer et al., text Servomechanism Fundamentals, 1st ed., chap. II, pages 20-38 (esp. pages 30 and 38), published by McGraw-Hill 00., New York City, 1947. 

